OAK FERN. 
129 
The roots are black and fibrous ; the rhizoma black, wiry and 
creeping, often, when long established, forming a dense matted 
mass. The young fronds make their appearance in March and 
April, each at first resembling three little balls on wires, pre- 
senting a very curious and excellent diagnostic ; these three 
balls gradually unfold, and display the triple character of the 
frond. The fronds soon arrive at maturity ; I have found them 
loaded with ripe seed as early as June : before winter they have 
usually entirely disappeared. The common stem is very slen- 
der, dark purple and shining, and is frequently twice as long as 
the frond ; it has a few scattered scales towards the base. The 
frond is triple, or composed of three distinct triangular portions, 
each of which has a short but distinct stem, and these three 
unite with the common stem at an obtuse angle, as represented 
in the figure at page 123. Each division of the frond is pinnate, 
and the pinnae are opposite, pinnate at the base, and pinnati- 
fid towards the centre, terminating in a somewhat acute apex ; 
the basal pinnules are sessile, and of nearly equal size, so that 
the four occurring at each union of the pinnae with the stem, 
form a cross. The mid-vein of each pinnule or ultimate division 
is sinuous, and the lateral veins are alternate and mostly simple, 
each terminates at the margin, and generally bears a circular 
cluster of dark brown capsules near its extremity : in some spe- 
cimens these clusters are so densely crowded as to form a margi- 
nal line, in others they are scattered and very distant. The 
fronds are of a most vivid and beautiful green, in this respect 
surpassing every other species with which I am acquainted : 
when of full growth and mature, they are alvrays fertile. In 
many specimens the frond is much more divided than the one 
which I have selected for my figure and description; and in 
such instances the veins and clusters of capsules partake of the 
subdivision. It should also be observed that the two lateral 
divisions of the fronds may, without impropriety, be termed the 
first pair of pinnae, in which case their divisions would be pin- 
nules, and not pinnae as I have here denominated them, from 
a desire to avoid a confusion of terms. 
In the cut at page 123, figure a represents a portion of the 
creeping rhizoma with three unexpanded fronds ; figure b an 
K 
